1. Field of the Invention
The present invention relates to a substrate processing method and a substrate processing apparatus, in which a peripheral edge of a substrate such as a substrate for a semiconductor wafer, a substrate for an optical disk, a substrate for a magnetic disk, or a substrate for a magnetooptic disk can be subjected to processing using a processing liquid.
2. Description of the Related Art
In the steps of manufacturing a semiconductor device, so-called bevel etching for rotating a semiconductor wafer (hereinafter merely referred to as “wafer”) having a thin film formed on its one surface with the wafer held approximately horizontally, supplying an etchant to the other surface of the wafer, and causing a part of the etchant to flow around to the one surface at a peripheral edge of the wafer to etch a peripheral edge of the thin film is carried out.
FIGS. 11(a), 11(b), and 11(c) are schematic cross-sectional views for explaining a conventional method of bevel etching.
A wafer W to be processed has a thin film F such as a metal film, for example, formed from its one surface to its end surface (peripheral surface), and particles P produced at the time of forming the thin film F adhere to a surface of the thin film F.
First, the wafer W is held approximately horizontally with the surface on which the thin film F is formed directed upward, and is rotated around its central axis C. An etchant L is discharged toward the vicinity of the center of a lower surface of the wafer W. The etchant L expands along the lower surface of the wafer W by a centrifugal force caused by the rotation of the wafer W, to be spun off sideward at a peripheral edge of the wafer W. Each of the surfaces of the wafer W and the thin film F has a wettability with the etchant L. Accordingly, a part of the etchant L flows around to the upper surface of the wafer W at the peripheral edge thereof (see FIG. 11(a)). Consequently, the thin film F on the end surface of the wafer W and at the peripheral edge of the upper surface thereof is etched away.
Thereafter, deionized water D is supplied from the center of the lower surface of the wafer W, thereby cleaning the lower surface of the wafer W. At this time, a part of the deionized water D flows around to the peripheral edge of the upper surface of the wafer W as at the time of etching (see FIG. 11(c)). Consequently, the end surface of the wafer W and the peripheral edge of the upper surface thereof are also cleaned.
However, the following problems occur in such a method.
The first problem is that contaminants caused by processing with the etchant L are produced at the peripheral edge of the wafer W. The wettability of the thin film F with the etchant L differs from the wettability of the wafer W with the etchant L. For example, even if the thin film F has a suitable wettability with the etchant L, the exposed wafer W may, in some cases, have water repellency to the etchant L. When the thin film F is removed by etching, therefore, a width along which the etchant L flows around to the upper surface of the wafer W may, in some cases, be reduced.
In a region where the width along which the etchant L flows around to the upper surface of the wafer W is reduced (hereinafter referred to as “retreat region”) B, an etching residue R is produced. Further, a crystallized product S obtained by crystallizing a component of the etchant L may, in some cases, be produced in the retreat region B (see FIG. 11(b)). The etching residue R and the crystallized product S may cause particle contamination and metal contamination, to contaminate another apparatus or cause a device obtained from the wafer W to develop a fault.
The second problem is that it is difficult to completely remove such contaminants produced in the retreat region B of the wafer W. When an attempt to remove the etching residue R and the crystallized product S by cleaning processing, a cleaning liquid must be efficiently supplied to the retreat region B.
Particularly when the surface of the wafer W is a hydrophobic (water-repellent) surface, however, the retreat region B (the exposed wafer W) may, in many cases, have a low wettability with not only the etchant L but also the cleaning liquid such as the deionized water D. Even if the cleaning liquid is supplied from the reverse surface of the wafer W, therefore, the cleaning liquid does not flow around to all portions of the retreat region B.
It is possible to adjust an amount in which the cleaning liquid flows around to the upper surface of the wafer W by changing conditions such as the number of revolutions of the wafer W. Even by such a method, however, it is difficult to completely remove the etching residue R and the crystallized product S. In order to completely remove the etching residue R and the crystallized product S, a long time period is required to clean the wafer W.
When an attempt to efficiently supply the cleaning liquid to the retreat region B is made, because the step of removing the etching residue R and the crystallized product S must be carried out using an apparatus other than an apparatus for performing etching processing, the whole step is complicated.
The third problem is that the cross-sectional shape of a peripheral edge of the thin film F is rounded. Even if the supply of the etchant L to the wafer W is stopped upon completion of the etching processing, a part of the etchant L remains at the peripheral edge of the wafer W, an end of the thin film F, and so on. In this state, when the deionized water D is supplied to the lower surface of the wafer W by adjusting the conditions such that an amount in which the deionized water D flows around to the upper surface of the wafer W is increased, the deionized water D flows around to the upper surface of the wafer W while dissolving the etchant L at the peripheral edge of the wafer W.
Therefore, a front end (a portion in contact with the thin film F, which is indicated by hatching in FIG. 11(c)) J of the deionized water D flowing around to the upper surface of the wafer W contains the etchant L at a high concentration. Therefore, the peripheral edge of the thin film F is etched, so that the cross-sectional shape of the peripheral edge of the thin film F is rounded.
The fourth problem is that the contaminants such as the particles P adhering to the surface of the thin film F cannot be removed. In the above-mentioned method, the deionized water (cleaning liquid) is not supplied to a large part, on the upper surface of the thin film F, of the wafer W. Accordingly, the particles P on the thin film F remain without being removed. In order to remove the particles P, the wafer W must be cleaned by another apparatus before or after the bevel etching is carried out.